In mobile communication and data processing equipment, the generation of audible sound, buzz tones or vibration are handled by systems mostly driven by electromagnetic actuators.
Sound is usually generated by, albeit small, voice-coil driven loudspeakers, whereas number of reasonably inexpensive and effective constructions have evolved for providing signal units to generate the necessary tones or vibrations for these devices. These include miniature motors with imbalanced rotors to create a sensible vibration; small piezoelectric assemblies to vibrate at an audio frequency and create a tone or beep (“buzz”) noise; and other, older technologies such as speakers with an electromagnetic voice coil, or a magnetic solenoid driving a diaphragm or other sound emitting element to create a sound such as an audio tone or a vibratory buzz. Many of the current mobile phones use separate components for vibration alert, audio alert and speech or music reproduction.
Also, it is desirable for most portable devices to a have a “hands-free” mode, i.e., a mode that allows a user to communicate through the device without having to use his or her hands. In order to operate portable phones in a hands-free mode, a high power output is required over a frequency range of 300 to 3400 Hz, often referred to as the speech band. At present the hands-free mode of commercially available products is exclusively implemented through common electro-dynamic or moving coil loudspeakers.
In a preprint of the Audio Engineering Society (AES) for the AES 108th Convention, Paris, 2000 Feb. 19-22, Preprint No. 5160, A. Bright et al. describe in details the problems surrounding any attempt to use a single component to perform vibration alert, audio alert and speech or music reproduction. The authors suggest such devices based on the common electro-dynamic loudspeaker or voice coil system.
A number of piezoelectric alerting devices have been proposed to generate a vibration or non-audible alert or audio frequency vibration and, thus, constituting a speaker. Examples of such devices are described in the U.S. Pat. Nos. 5,514,927; 5,368,456; 6,078,126 and 6,169,206.
In view of the above, it is the purpose of the present invention to provide a loudspeaker for electronic devices, particularly portable electronic devices such as mobile phones, which is compact, lightweight, provides sufficient sound for hands-free operation but does not present a sound hazard to the listener if held close to the ear. It is a further object of the invention to provide a space- and energy-efficient device and method for generating a tactile or vibratory alarm and audible sound.